Non-toxic aluminum enamel frits



United States Patent NON-TOXIC ALUMINUM ENAMEL FRITS 2,911,312 Patented Nov, 3, 1959 550 C., at least 70% by weight of said frit consisting of 22-35% by weight TiO, 14-29% by weight S103 5 17-26% by weight N3 0 Lewis C. Holfman, Scotch Plains, N.I., assignor to E. L 13% by weight L1 0 :11 Pout dauNenfiolgl-slaand Company, Wilmington, DeL, i i containing less than e 4.0% by weight A1 0, N0 Drawing. Application Janu 7 1957 110% y weight 1 Serial No. 632,662 an 10 30.0% by weight BaQ 4.0% by weight C30 6 Claims. (Cl. 106-48) 1.0% by weight C00..-

0.5% by weight CdO 11.0% b wei ht K 0 This invention relates to new non-toxic aluminum 0.1% byz weigh t M116 enamel frits. More particularly, it relates to the forma- 1% by weight o tron on aluminum and aluminum alloy articles of hard 05% by weight p o vitreous enamel coatings which will be non-toxic in use, 10% by weight o and 1111912 certfain improved novel vitreous enamel frits to 43% b weight 1:0

itreo tl s ha r r l l imme for. use in the vitreous All percentages 9f mgredlems at? exprfifssedlm weight enameling of aluminum and aluminum allo surfaces percent for convemence companson with Pnor an are described and claimed in De U 8 Patent Although the enamel fr1ts above characterized are en- No 2467114 Such enamel gg W0 tirely suitable for the formation of protective, adherent wid'c 1 i feat Success D 0 18 and attractive enamel coatings on aluminum and alumig g 4 eymp an e num alloys, there is sometimes evidence of corrosion of have even been used for enameling outer surfaces of th I f d th fi S h aluminum cooking utensils. They have not been ape al-lmmum sur ace e rlngoperanon' c proved for the enameling of the interior surfaces of such cormslon appears t9-be the rqsu-lt of Dameutensfls use of possible toxicity when contacted for lar enamel composition of th1s invention s1nce 1t does not prolonged periods with certain acidic foodstuffs It has appear 1n the fir1n g of the Deyrup enamels wlnchcontam been. I] filed that the presence of the substantial lead substantial quantities of lead oxide. I have now dl8 content of the Deyru enamels might lead to toxici y to ct-wered that this cormsmn dunng finng efldi-mced by v: sensitive whenacidic food mfi are left to shght unevenness of coated surface, can be ehmmated by i in such g 8 addition to the frit composition, before melting, of 1% Attempts made heretofore to produce a satisfactory to 11% It therefor? generally preiened thait vi enamel hit for the enameling of aluminum and such quantity of ant1mony oxlde be molten 1n the fat aluminum alloys without the use of a substantial quantity Fomposlimn' 'i the amount of sbaos melted of lead have been unsuccessful A satisfactory enamel m the fm composltwn W111 be 1% and k amount required will depend upon e alkali content 0 gi gg fi gfi g fi z g g 553 3 2,: gg the frit, the amount of chromate pretreatment that the berm alumina! and musgt z a tempergwre aluminum surface is subjected to, and whether the surface is substantially pure aluminum or the aluminum zigzag $533 appmachmg that of alummum and content if an aluminum alloy. The lower the alkali cona tent of the frit the lower may. the S1330, content be to It 13 an ob ect of th1s mvention to produce a substan- 0bta1n a given effect. Tables 1 and 2, below, show preg gz g' g g z g zg zgg zfi fii g g fzzf ferred exemplary enamel frit compositions in weight f thi t percent and mol percent, respectively. Table 3 discloses t er o 16:t o 0 5 a F weight percent composition of batches for the production factory Qlethod of enamellflg alumfnum and a-hfmlnum of the respective enamel frits shown in Tables 1 and 2. alloys Wlth such 5 9 11911401510 enamel It is to be understood that other suitable batch compoother oblwts 0f mvelftlon W111 pp herfilnaftelfi 5 sitions may be used in making the respective frits of Ta- The objects of th1s mvent1on may be aecompllshed by bles 1 and 2, the raw materials being calculated to yield. the preparation of a non-toxic, substantially lead-less the desired frit composition.

TABLE 1 [Weight percent] TotalR,0-- 322 33.9 31.9 31.9 29.3 30.7 23.6 30.4 32.2 25.8 32.0 29.2 35.9 39.0

020 1.2 3.3 BaO 10.4 10.9 10.2 10.2 12.6 11.1 13.6 9.7 18.7 30.3 11.2 11.3 ZnO 2.0

Total R0 11.6 10.9 10.2 10.2 12.6 13.1 13.6 0.7 13.7 30.3 11.2 14.6

.4140 3.5 11,0. 6.5 1.7 1.6 1.6 9.7 9.7 10.5 1.5 1.7 1.7 7.2 smo, 1.7 1.6 1.6- 1.9 21 1.5 1.7 1.7 1.3 1.

Total 11401---- 6.5 3.4 3.2 6.7 11.6 9.7 12.6 3.0 3.4 3.4 9.0 1 8 TotalR01.. --'49.0 51.8 M? 51.2 4114 46.5 50.3 56.9 49.2 422 53.4 53.9 55.1 60.2

g ams" 330 dn gallons-..

in preparing a enameling with the enamels of this invention NaOH factory for use Kgclgoq '2( 4)s Water TABLE 2 (Molpercenfl 2 u u A .1 3 W 1 m .u 0 M w L 190 0 m m 4 06 Am m m m m 7 %M M m m 375 23 5 1 36 9 m LIMA a 4:0 nm 2 n 3 .1 a 1 s 1 4 5 5 m .m 2 m 1 975 1 4 4 m AJ 5 6 & MW 1 m M m Wm M 1 040 4 2 2 m 0 4 A 4%7 "m 9 9 m a 142 a e n m m m 3%? M A 4 2 M m w M m t 26 m 8 5 5 6 47 J A w n m w s. a n on m T m 64.7 7 1 2 82 0 a 1. m n w 778 2 1 1 9 17 m 8 l fid fi 6 6 965 0 0 0 6 4 9 3 m 5 5 1 mm 9% 2 0 0 2 1 1 11 1:1 11 x 5 5 2 mm. m m m m m m 299 0 2 n 2 2 70 7 n n "nmfi n n n 1 3 o n 9 1 w 1 M 1m1xw 1 1 C uh1 4 59 4 7 7 06 6 m N18 n 0A M 11141 61 61 81 11 oB .m(01(N a 1 mm 5 T n 1 sumo. mm 1 o um 1 1 1 1 1 1 1 1 1 mo a 7o om 1 1 1 1 1 .1 1 1 1 1mmm mnm m 1 o 1 1 1 1 m ouowmu m n R 1 R 1 1 R 1 1 R m m umwmm M 11 1 (A n M m a m r. M mmmwmmm m T in T m T wmm T mmim m maw am 052 as sTz FBTBwznAzs Ls In preparing the frits, the batch is weighed, mixed, and heated in a crucible until completely melted to a homogeneous mass. Crucible temperatures may vary from 900 C. to 1200" C. The molten glass is fritted by running the molten mass into water which causes a The frit may be dried at about 50 C. or less to shattering of the glass into small particles to form the frit.

The aluminum article is immersed in this bath, heated to a temperature of 60 C., for a period of two to ten minutes. The pretreated surface is then preferably fired for a period of two to thirty minutes at a temperature between 480 C. and 580 C. The optimum conditions as white or colored pigments, opacifying agents, or the of chromate pretreatment and firing will depend largely upon the composition of the aluminum alloy to be treated. In the case of any particular aluminum alloy, it can readily be determined whether or not sufficient enamel adherence to insure against water-spalling is obtained by is can be determined by means of the following accelerated test which correlates with water exposure results which may take weeks or months. This accelerated test consists in chromale-treating and enameling pieces of the particular alloy Such vehicles are, for exto be tested, and then exposing the enamel-metal interface by gouging, filing, or scratching the same, and immersing the test sample in 5% aqueous ammonium chloride solution for ninety-six hours at room temperature. If no failure occurs back one-ei hth inch from the enameled are first cleaned, if necessary, by treatment edge of the exposed interface, excellent performance in water exposure will result from the chromate treatment and enameling conditions used. The particular optimum treatment and enameling conditions for a specific alloy can thereby be established. Once optimum treatment treatment of the aluminum surface is slightly more drastic conditions for a given alloy have been established and a chromate bath is used for continued treatment of the alloy structures or articles, it will, of course, be desirable to periodically analyze the treating bath and keep the chromate content and alkalinity of the bath within spraying, dipping, 55 any prescribed course of treatment. Th Any air-dry or thermo-fluid The surfaces Preferably, the chromate prefarably above about 10%, ex-

ir initial value.

For example, the followhromate pretreatment has been found very satisafew percent of the rr Sh d rc Pd 6 .5 m m m mm b 2 M S r m O S a f m u u e w e m o s 0 m1 t m m o l.m m m s 0 s no. at 11 0 e a m :7 e U f. n a 8 e n 6 S C a e br.ma m w .w .w m a m Pt m a n m m m w m m m m n m t e 1 e c o m g 0 m2 5 .1 1 i a m s s a e n g 1msu n v. mi mm d 0 u ed a s s m o u o b mr mkv. 8 s um d n H n m. .m o k em co me i o mP n g h .m m W .m a n tar. c g b O. n .1 c Y nm n n es W8 h e e vm m r m m m4 OW? m m a n .5 0 s a o m m m. a g m w mm w m .m e 1. mm c m .UO w m mw irv 3 Dawn C I-l mwmw .s w m m 9 m m mcmmnme wlrk w mmv m o mmmn k n e yum .B m m .m C. U C m r. 4 h re m d n h s I Pe4 u s mmm m o v c mm w mwm m mm m e s e o o s 7.1 2 F WE m R m "M I em t t. O r m M a t. m a a O H f nf 7 e n m P n e n. ,r 0 hm m .nM m /8m ooi 6.m Um M a h m ck w ed m .1 .m m m nz .m N. m M 1 wmrmm m nmm n mmm Tm m s m m mmmm mwn mw mmmm e a m mmw m. .msawm mmz... ma map ingc After application of the enamel to the aluminum or aluminum alloy, it is fired in a suitable furnace in order to fuse the powdered enamel to a continuous glossy coating. The firing conditions are not critical, except that the article must be brought to a temperature high enough to melt the enamel but not so high that the metal article will be injured. The temperature necessary de pends to some extent on the particular aluminum alloy being enameled and upon the particular enamel composition being used. It is not generally necessary to employ'a temperature above about 550 C. and, inmost cases, the enamel may be satisfactorily fused at a temperature between 490 C. and 550 C. It is merely necessary to keep the article a t'the selected temperature for a few minutes to permit the enamel to fuse completely to a uniform, adherent, vitreous layer. Several coats may be applied, if desired.

The enamels of this invention have surprisingly low fusion points despite the fact that they do not contain any substantial quantity of lead. Moreover, these enamels have a degree of resistance to chemical agents which was not believed possible for a substantially lead-free enamel.

Furthermore, these enamels adhere exceedingly well to aluminum or aluminum alloy surfaces even when exposed to thermal shocks or considerable mechanical flexing of the metal. The following examples are given to illustrate certain preferred procedures for the enameling of aluminum and aluminum alloys.

Example I Aluminum alloy sheet stock composed of aluminum alloy 61 (containing, by weight, 0.25% copper, 0.6% silicon, 1.0% magnesium, and 2.5% chromium) is immersed for two minutes in a bath heated to 60 C. and consisting of the following:

NaOI-I g ams-.. 330 KgCl'gOq (In a( 4)s Water gallons.-- 1

1.6% by weight Li O 20.9% by weight Na o 9.7% by weight K,0 1.2% by weight CaO 10.4% by weightBaO 6.5% by weight 8,0, 23.4% by weight SiO, 26.2% by weight TiO,

The liquid and solid contents of the slurry are mixed in such proportions that the sheet after dipping in the slurry and draining will contain approximately 0.5 gram per square inch of surface. The enamel is fired at a temperature of 500 C. for nine minutes. The resulting enamel will have optimum properties; for example, it will be glossy and of a pleasing white color, which will adhere tenaciously to the substrate in life testing and in accelerated testing and it will be substantially unaffected by 10% citric acid in fifteen minutes, and will resist indefinitely the attack of a 10% household detergent solution at boiling temperature.

Example II The process of Example I was repeated using a chromate pretreatment solution containing and the use of a frit having the following composition:

1.7% by weight Li O 22.0% by weight Na,0 10.2% by weight'K o 10.9% by weight BaO 1.7% by weight B 0,

1.7% by weight Sb O 24.4% by weight SiO 27.4% by weight TiO,

The other conditions of Example I were followed as set forth in that example. The results were approximately identical to the results therein set forth.

Throughout the specification and claims, any reference to parts, proportions and percentages refers to parts, prolpgrtions and percentages by weight unless otherwise spec- Since many changes and modifications can be made in the above described details without departing from the nature and spirit thereof, it is to be understood that this invention is not to be limited except as set forth in the appended claims.

I claim:

1. A non-toxic vitreous enamel frit having a maturing temperature of 490 C. to 550 C. suitable for the enameling of aluminum and aluminum alloys at least 70% of which consists of 22% to 35% TiO, by weight 14% to 29% SiO, by weight 17% to 26% Na,0 by weight 1% to 3% Li=0 by weight said frit containing less than 0.1% NiO by weight 0.1% MnO by weight 1.0% C00 by weight 4.0% A1 05 by weight 11.0% 13,0, by weight 2.0% ZnO by weight 30.0% BaO by weight 4.0% CaO by weight 4.0% ZrO, by weight 0.5% PbO by weight 11.0% K 0 by weight said frit consistingvessentially of the above-named ingledients, all of which are melted together to form the 2. A non-toxic vitreous enamel frit having a maturing temperature of 490 C. to 550 C. suitable forthe enameling of aluminum and aluminum alloys at least 70% of which consists of 22% to 35% TiO, by weight 14% to 29% SiO, by weight 17% to 26% Na,0 by weight 1% to 3% Li,0 by weight said frit containing less than surface of aluminum and aluminum rich alloys which enamel having a maturing temperature of 490 C. to 550 comprises fusing thereon a vitreous enamel frit having C. at least 70% of said enamel consisting of a maturing temperature of 49 C. to 550 C. at least 22% to 35% Tie: by weight 70% of said enamel frit consisting of 14% to 29% Sic: by weight 22% to 35% TiO: by weight 17% to 26% Na,0 by weight 14% to 29% SiO, by weight 1% to 3% Li O by weight 17% to 26% Na o by weight 1% m 3% up b weight Hamel :2 g km o 1 y wet sand frit contarmng less than 30 0.1 Mao by weight 0.1% NiO by weight 1.0% CoO by weight 0.1% MnO by weight 4.0% A1 0; by weight 1.0% C00 by weight 11.0% B 0, by weight 4.0% A1 0, by weight 2.0% ZnO by weight 11.0% B 0, by weight 30.0% BaO by weight 2.0% ZnO by weight 4.0% CaO by weight 30.0% BaO by weight 4.0% ZrO, by weight 4.0% CaO by weight 0.5% PhD by weight 4.0% ZrO, by weight 11.0% K 0 by weight 3'32: 33?; said enamel consisting essentially of the above-named I y ingredients, all of which are melted together to form the said frit consisting essentially of the above-named inmt the l gredients, all of which are melted together to form the i and zilummum 99 alloy frit mg a protecuve coating comprising a non-toxic vitreous enamel having a maturing temperature of 490 C. to

A process for applymg women" 8 on the 550 C. at least 70% of said enamel consisting of surface of aluminum and aluminum rich alloys which comprises fusing thereon a vitreous enamel frit having 22% to TiO, by weight a maturing temperature of 490 C. to 550' C. at least 14% to 29% SiO, by weight of said enamel frit consisting of 17% to 26% Na=0 by weight 227 t 35% To b gm 1% to 3% Li,0 by weight a o 1 a y wei 14% to 29% Sio2 by weight said enamel containing less than 17% to 26% Na o by weight 0.1% NiO by weight 1% to 3% Li O by weight 0.1% MnO by weight 1.0% C00 by weight said frit containing less than 4.0;: A1 0, by weight 11.0 a 0 b wei t 0.1% NiO by weight 29% 23 g gf 01% M by 9 40 30.0% BaO by weight 19% CO0 by 5 4.0% CaO by weight 49% by "9 4.0% 2:0, by weight 11.0% B303 by Weight 05% o by weight 2.0% ZnO by weight 11.0% K,O by weight 30.0% BaO by weight 45 43% CaO by weight said enamel consisting essentially of the abovemamed 1n- 4 21.02 by weight gredients, and as an agent to prevent corrosion dunng 05% pbo by weight firing of the enamel between 1% and 11% S11 0, all of which said ingredients being melted together to form the enamel frit.

References Cited in the tile of this patent 11.0% K 0 by weight said frit and consisting essentially of the above-named ingredients, 'and as an agent to prevent corrosion during firing of the enamel between 1% and 11% Sb O, all UNITED gnu-Es PATENTS of said ingredients being melted together to form said 2,414,633 Bryant Jan. 21, 1947 frit. 55 2,660,531 Fraser et al Nov. 24, 1953 5. Aluminum and aluminum rich alloy articles contain- 2,662,020 Schofield et a1. Dec. 8, 1953 ing a protective coating comprising a non-toxic vitreous 2,753,271 Treptow July 3, 1956 Notice of Adverse Decision in Interference In Interference N0. 92,7 58 involving Patent No. 2,911,312, L. C. Hoffman, NON-TOXIC ALIMINUM ENAMEL FRITS, final judgment adverse to the patentee was rendered May 31, 1966, as to claims 1 and 2.

[Oyficial Gazette December 13, 1966.]

Disclaimer 2,9 1 1,312.Lewis C. Hoffman, Scotch Plains, NJ. NON-TOXIC ALUMI- NUM ENAMEL FRITS. Patent dated Nov. 3, 1959. Disclaimer filed. Aug. 12, 1966, by the inventor and the assignee, E. I du Pom? de Nemou/rs and Company.

0 claims 1 and 2 of said patent.

Hereby enters this disclaimer as t [Ofiicial Gazette Deaembev" 20, 1966.] 

0.1% NIO BY WEIGHT 0.1% MNO BY WEIGHT 1.0% COO BY WEIGHT 4.0% AL2O3 BY WEIGHT 11.0% B2O3 BY WEIGHT 2.0% ZNO BY WEIGHT 30.0% BAO BY WEIGHT 4.0% CAO BY WEIGHT 4.0% ZRO2 BY WEIGHT 0.5% PBO BY WEIGHT 11.0% K2O BY WEIGHT
 1. A NON-TOXIC VITREOUS ENAMEL FRIT HAVING A MATURING TEMPERATURE OF 490*C. TO 550*C. SUITABLE FOR THE ENAMELING OF ALUMINUM AND ALUMINUM ALLOYS AT LEAST 70% OF WHICH CONSISTS OF 